13.—(1) With the leave of the Tribunal, the appellant may amend his notice of appeal or deliver supplementary grounds of appeal.
(2) Rule 8(5) applies to an amended notice of appeal and to supplementary grounds of appeal provided under paragraph (1).
(3) With the leave of the Tribunal, the Secretary of State may amend or supplement the material which he has provided under rule 10 or 11.
(4) Where further objections are provided under paragraph (3), the Tribunal shall consider them in accordance with rule 12.